Department of Chemistry, National Institute of Technology (NIT), J&K, Srinagar 190006, India.
iDREAM (Interdisciplinary Division for Renewable Energy & Advanced Materials), NIT, Srinagar 190006, India.
ACS Appl Mater Interfaces. 2022 Jan 26;14(3):4690-4698. doi: 10.1021/acsami.1c20463. Epub 2022 Jan 5.
Numerous fascinating hierarchical surfaces from nature, including cactus spines, rice leaves, Namib desert beetle, spider silks, and pitcher plants, have been thoroughly investigated to emulate and architect superior surfaces for capturing sustainable, clean, and safe freshwater from the atmosphere. Hitherto, the adaxial side of biological surfaces has been meticulously investigated for wettability and atmospheric water harvesting (AWH) applications. However, the abaxial face has not yet attracted much scientific scrutiny. Here, we revealed the multifunctional Janus surface traits of (i.e., red clover) leaf with extrusive atmospheric water fishing ability on both adaxial and abaxial faces. Water harvesting is performed by conical outgrowths (microhairs). The individual hair's intriguing topography comprises asymmetric shape and surface roughness, which plays synergetic roles in water deposition and directional transport. The water collection quantity on the leaf surface is a function of hair density, which varies significantly on two sides. Noticeably, instead of gravitational pull, the hairs perform water reaping competence under the collective impact of surface energy and Laplace pressure gradients. Consequently, both straight-up and upside-down water harvesting are presented. Furthermore, the leaf surface exhibits dual water wettability features. The upper side manifests the water-repelling and water roll-off phenomenon. In contrast, the lower surface displays a water-retaining/or pinning effect. Optical microscopy, scanning electronic microscopy, real-time optical visualization, and contact angle analysis were employed to characterize the natural and template specimens. The dorsiventral asymmetry of the leaf examined in this work could be helpful for a plethora of applications, such as scalable AWH, rainwater collection, self-cleaning, and adhesive fixtures.
自然界中存在许多令人着迷的分层表面，包括仙人掌刺、稻叶、纳米布沙漠甲虫、蜘蛛丝和猪笼草，这些表面都经过了深入研究，以模仿和构建优越的表面，从而从大气中捕获可持续、清洁和安全的淡水。迄今为止，人们已经对生物表面的叶面进行了细致的润湿性和大气水收集（AWH）应用研究。然而，叶背却尚未引起科学界的太多关注。在这里，我们揭示了（即三叶草）叶片的双面 Janus 表面特性，其叶面和叶背都具有突出的大气水收集能力。水收集是通过圆锥形的突起（微毛）来实现的。单个毛发引人入胜的形貌包括不对称形状和表面粗糙度，它们在水的沉积和定向传输中协同发挥作用。叶片表面的集水量是毛发密度的函数，而毛发密度在两面有显著差异。值得注意的是，毛发不是在重力的作用下，而是在表面能和拉普拉斯压力梯度的共同作用下，表现出卓越的集水能力。因此，既能实现正向集水，也能实现倒置集水。此外，叶片表面还表现出双重的润湿性特征。上表面表现出疏水和滚落现象。相比之下，下表面则表现出保持水或固定水的效果。我们采用光学显微镜、扫描电子显微镜、实时光学可视化和接触角分析对自然和模板样本进行了表征。本工作中研究的三叶草的背腹不对称性可能有助于实现多种应用，例如可扩展的 AWH、雨水收集、自清洁和粘附固定装置。
